Hubble spots surviving companion to supernova 17 years later

"We were finally able to catch the stellar thief, confirming our suspicions that one had to be there," said Berkeley astronomer Alex Filippenko.

Seventeen years after the initial stellar explosion, astronomers were able to locate the surviving companion to a supernova. Photo by Hubble/NASA/ESA

April 27 (UPI) -- The Hubble Space Telescope has captured the best evidence yet that double-star systems host supernovas.

Seventeen years after astronomers first spotted a supernova 40 million light-years away in the galaxy NGC 7424, a Hubble photograph revealed a second star, the supernova's surviving companion.

"We know that the majority of massive stars are in binary pairs," Stuart Ryder, researcher at the Australian Astronomical Observatory in Sydney, said in a news release. "Many of these binary pairs will interact and transfer gas from one star to the other when their orbits bring them close together."

The companion in Hubble's image was more than just a spectator to the action 17 years ago. The companion is a cosmic criminal, guilty of theft. Millions of years before its companion exploded a fire death, the star was creating instability in the primary star by siphoning off hydrogen from its stellar envelope, the layer that shuttles energy from the core to the star's atmosphere.

As a result of millions of years of theft, the primary star demise, dubbed SN 2001ig, was classified as a Type IIb stripped-envelope supernova, an explosion characterized by a lack of hydrogen.

Most scientists thought Type IIb stripped-envelope supernovas originated in single star systems, their out envelopes blown away by strong stellar winds. But over the years, astronomers have struggled to find the primary stars responsible for such explosions.

"That was especially bizarre because astronomers expected that they would be the most massive and the brightest progenitor stars," said Ori Fox of the Space Telescope Science Institute in Baltimore. "Also, the sheer number of stripped-envelope supernovas is greater than predicted."

Astronomers now think as many as half of all Type IIb stripped-envelope supernovas may originate in binary star systems.

The revelation might not have happened if SN 2001ig occurred just a little farther away. The stellar system sits right on the edge of Hubble's photographic limits. The companion is so faint, it likely would be invisible to Hubble if it was a few more light-years away. A bit of luck allowed for the breakthrough.

"We were finally able to catch the stellar thief, confirming our suspicions that one had to be there," said Alex Filippenko, astronomer at the University of California, Berkeley.